Rapisardi, co-investigator of this proposal, has been studying the synaptic organization of the dorsal lateral geniculate nucleus (DLGN) through reconstructions of serial electron micrographs. From his studies we suggest that synaptic triads are more characteristic of the X than of the Y system. This hypothesis could be tested if the electrophysiology of the reconstructed neurons were known. Therefore, the long-term goal of this project is to directly correlate the synaptology and electrophysiology of X and Y cells in DLGN, DLGN neurons will be extracellularly identified as X or Y cells according to (1) their response latencies to optic chiasm stimulation, (2) their response latencies to antidromic stimulation of cortical areas 17 and 18, and (3) their linearity to spatial summation. After intracellularly labeling identified neurons with horseradish perosidase (HRP), the cell's morphology will be studied at the light and electron microscopic levels. The synaptic relationships of labeled neurons will be reconstructed through serial electron micrographs and correlated with the electrophysiology of the X and Y systems as observed at the DLGN. These studies will be important in determining what, if any, transformations of the X and Y systems occur in the DLGN. The proposed experiments constitute a pilot study for a larger project. The purposes of the proposed experiments are (1) to gain experience and equipment necessary to electrophysiologically identify DLGN cells, and (2) to develop the capability intracellularly inject with HRP identified cells. The synaptic relationships of filled cells will be investigated with serial electron micrographs (a technique currently in use in our laboratory) resulting in publishable data. This proposal will help a new investigator to change research directions from intracellular studies of the basal ganglia to the visual system.